1. Field of the Invention
This invention relates generally to serially advancing articles and more particularly to a method and apparatus for detecting jam-ups of such advancing articles and stopping the advancement thereof in response to detection of a jam-up.
2. Brief Description of the Prior Art
In the manufacture of paperboard blanks for making finished boxes therefrom, it is customary to advance the flat blanks from a printing and slotting or diecutting machine through a folder-gluer machine which applies adhesive to one edge thereof and folds the blank along score lines therein to form flat tubular carton blanks which may be stacked and tied into bundles for shipment. An example of such a folder-gluer machine may be found in Lopez U.S. Pat. No. 3,122,069. Jam-ups of blanks frequently occur in such machines due to imperfect score lines, blank slippage and the like. Often such jam-ups go undetected until several blanks become jammed in the machine and which may take several minutes of production time to clear and sometimes damages the machinery. Accordingly, it is beneficial to have a detection system to detect such jam-ups and stop the machine before many blanks become jammed and even to detect an impending jam.
Many efforts have been made to provide a jam detection system suitable for operation with modern, fast-moving machinery. One notable example is found in King U.S. Pat. No. 3,311,224 which measures the spaces between the advancing blanks and stops the machine if the spaces become too short indicating that a jam is about to or has occurred. Unfortunately, this system depends on the space between blanks being constant for all sizes of blanks whereas most box making machinery is adjustable to cyclically feed different size blanks within a preset range. The nature of the feeding cycle results in a greater spacing between blanks when the blank size is shorter than the maximum size that can be processed by the machine. Thus, the system devised by King does not appear capable of detecting jams when the space between blanks is not constant for all blank sizes. The Grover and Broido patents mentioned in the King patent are of interest with respect to other systems for detecting jams. The patents cited in the prosecution of the King patent are of interest only insofar as they illustrate various isolated elements that might be combined for specific purposes.
Accordingly, it is an object generally of the present invention to provide a system for detecting jam-ups of serially advancing blanks and more particularly for detecting actual or impending jams independently of the size of the spaces between blanks or the length of such blanks being run.